The present invention relates to a fingerprint recognition device, and more particularly to a fingerprint recognition device capable of making a more definite fingerprint recognition by using a hologram.
A conventional fingerprint recognition device as shown in FIG. 1 consists of:
an LED(liquid electroluminescence device)array plate 1 as a source of light which is directed onto the fingerprint of a finger,
a prism 2,
an image-forming lens system 3 for forming an image of a fingerprint on the inclined surface of the prism 2,
an area charge coupled device (in short, an area CCD) 4 for converting the fingerprint image formed by the image-forming lens system 3 to electrical signals, and
a circuit 5 for amplifying and analyzing the electrical signals from the area CCD 4.
When light is emitted from the LED array plate 1 onto the inclined surface of the prism 2 on which a finger makes contact, the above-mentioned fingerprint recognition device forms a fingerprint image on the inclined surface of the prism 2 by making the convex portions of the fingerprint of the finger bright since those portions contact the inclined surface of the prism 2 and making the concave portions of the fingerprint of the finger dark since the portions do not contact the inclined surface of the prism 2.
Such a fingerprint image is formed on the area CCD 4 by means of the image-forming lens system 3 and then is converted to electrical signals to be transferred to the circuit 5 in which the electrical signals are amplified and analyzed to recognize the fingerprint.
As indicated in FIG. 2, however, the above-mentioned conventional fingerprint recognition device forms a slanted fingerprint image 6 on the area CCD 4 since the fingerprint image is formed on the prism 2 in a 45.degree.-slanted state with respect to the optical axis of the horizontally mounted image-forming lens system 3.
According to this, since the fingerprint image appears clearly around the optical axis but it becomes more defocused as one goes farther from the optical axis, the conventional fingerprint recognition device has problems in that image distortions and the like occur which make an accurate fingerprint recognition impossible.
And also, since the image-forming lens system 3 consists of a plurality of lenses in order to compensate for the above-mentioned problems to a certain extent, the conventional fingerprint recognition device has other problems in that as the volume of the optical system becomes larger, the manufacturing cost increases, and the like.